Digital micro-mirror devices (DMD) are capable of being used in optical communication and/or projection display systems. DMDs involve an array of micro-mirrors that selectively communicate at least a portion of an optical signal or light beam by pivoting between active “on” and “off” states. To permit the micro-mirrors to pivot, each micro-mirror is attached to a hinge that is mounted on one or more support posts coupled to a CMOS substrate. Beneath the micro-mirrors and support posts the CMOS substrate used to control the movement of the micro-mirrors of the DMD. Unfortunately, when the micro-mirrors are in the “off” state, this CMOS substrate, which is optically reflective, may be exposed. As light passes between the micro-mirrors of the DMD, it may then be reflected by the surface of the substrate, resulting in an unwanted optical artifact and limiting the contrast of the DMD.
A variety of methods have been employed in an attempt to reduce the reflectivity of the CMOS substrate that makes up the substructure of the DMD to improve the DMD's contrast. Some approaches have used multilayer dielectric structures made of materials such as SiO2 and TiN to cover the DMD substructure. This approach, however, is limited in its applicability due to the semiconducting nature of TiN, which may cause electrical issues such as charging and parasitic capacitance. Other approaches have employed chromium oxides over chromium or other reflective metals to form optical apertures used in some DMDs. This approach is also limited, as the use of chromium is highly restricted by environmental concerns. Finally, methods employing non-metallic elements have been limited due to the fact that non-metallic elements in exposed layers in the DMD tend to react with fluorine in the headspaces of the DMDs to form compounds having high partial pressures that can damage the DMDs.